Process for removing antimony from lead containing it



' Nov. 30, 1943. w.l T. MONsoN ErAL l 2,335,559

PROCESS FOR REMOVING ANTIMONYFROM LEAD CONTAINING'IT Filed n aarch 18, 1942 2 sheets-sheet 1 INV ENT @R5 VVE/ TEEv TMONSON. HqRoLo L.HUMES. f BY E/cHA en I? EHEEMSooe/ l ha( 756.; TroRNEYs ZLE/an y SLAG Nav. 43o, 1943.

w. fr. MNsoN ETAL Y 335569 PROCESS FOR REMOVING ANTIMONY FROM LE@ CONTAINING IT Filed March 18, 1942 2 Sheets-Sheet 2 or METALL/c Leno oe ANT/Mawr Pesse-Nr as ox/oss IN THA-,amaca BY .1E/cuneo EEZHERMJDQBE l /L/a-vc 7,6...14ITORNEY5 i Patented Nov. 30,1943 p UNITED STATES PATENT OFFICE PROCESS FOR REMOVING ANTIMONY FROM LEAD CONTAINING IT Walter T. Monson, Newark, Harold L. Humes,

Princeton,

and Richard P. E.

Hermsdorf,

Roselle, N. J., assignors to The American Metal Company,Y Limited, New York, N. Y., a corporation of New York Application March 18, 1942, Serial No. 435,148

6 Claims.

having as high antimony content as we are able 4 to produce in accordance .with our invention. Furthermore, we are able to remove antimony more rapidly on a commercial scale than by heretofore known processes.

We have found as an important part of our,

invention that antimony may be removed from -lead containing the same, but substantially no tin, by placing lead oxide containing not less than of antimony as oxide on a bath of the impure lead' in molten condition containing not less than 4% of antimony and stirring the molten impure lead and lead oxide at a temperature of the order of 1100-1200 F. to producel a slag containing antimony absorbed by the slag from the bath. The quantity of lead oxide employed is suiilcient to reduce the quantity of antimony so that an equilibrium point between the antimony of the bath and the antimony of the` slag is reached as shown on the chart, Fig. 4, mentioned below.- Equilibrium points at which more than 1.9% antimony in the bath and more than 38.5% antimony in the slag will occur are shown on the said chart, but in starting with the minimum amount of about 15% antimony in the required amountvof dross and about 4% antimony in the bath, the equilibrium point will not go below about 1.9% antimony in the bath and not below about 38.5% in the dross. In the appended claims, where the expression is used-an equi- `mony in the slag than 38.5%, but that no equilibrium lpoint will be reached at which the antimony content of the -bath and slag, respectively,

are below these figures.

'The process is preferably carried out in 'an apparatus shown in the accompanying drawings.

Thev drawings also include a chart givingl data as to slags occurring in the practice of the invention.

In the drawingsp Figure 1 is a vertical section shown in part diagrammatically of kettle with a stirrer mounted thereon;

Fig. 2 is an enlarged detailed plan view of the impeller of Fig. 1;`

Fig. 3 is an enlarged fragmentary sectional elevational of the impeller shown in Fig. 1; and Fig. 4 shows the above referred to chart. The apparatus shown is not part of our invention and other apparatus may be employed instead thereof. The chart, however,r as mentioned, is based on the actual operation of the process of the invention. y

Referring now to the apparatus in the drawings, numeral l indicates a hemispherical steel kettle in which is contained a bath 2 of molten impure lead containing antimony and arsenic, but no tin or substantially none. Mounted above the bath on suitable supports 3 is a high speed electric motor 4. This motor operates a vertical shaft 6 which depends therefrom and at the end of which is mounted a disintegrating impeller (i. The shaft and impeller are preferably covered with stellite to prevent corrosion by the molten materials of the bath and dross. The impeller is situated preferably at about half the depth of the bath 2. The motor 4 Vis capable of rotating the shaft and impeller. at speeds of 900 R. P. M. or higher, giving a peripheral speed of the impeller of over about 2,600 ft. per minute. The impeller 6 comprises a sleeve 1 keyed to the shaft 5 by key 8. From the collar and integral therewith extend four disintegrator radial arms 9 of generally elongated pyramidal shape in plan view. Each outer free end of each arm terminates inltwo flat disc-like faces I0 providing a bath is drawn into the vortex and from there thrown out laterallyl byv the impeller so that the particles thereof are disseminated through the the arsenic is low. The removal of arsenic may be carried out in accordance with the. process of copending application, Serial No. 433,464, filed March 5, 1942, of Max F. W. Heberlein and Richard Nevin Bierly. Briey, this last-mentioned process involves the removal of arsenic from impure lead by treatment of the lead in molten condition with caustic alkali in the absence of air or other oxidizing agent, the process being preferably carried on in a substantially air-tight kettle.

If our process is operated on metal containing arsenic, the slag iirst produced, that is, after running for, say, thirty minutes, will contain substantially all of the arsenic and this slag may be set aside for retreatment, viz., making antimonial lead with higher percentages of arsenic which may be marketed as such or from which arsenic may be removed by the aforesaid pending application. The slag thereafter, that is,

` formed following the thirty minute' run, Will be much lower in arsenic and will be used to produce material of very high antimony content. If the amount of arsenic in the metal is low or if the presence of arsenic in the antimony slag or other product is not objectionable, then no separation of the arsenic slag as mentioned above is necessary.

In order to operate our process, a supply of lithargeor slag containing lead oxide should be available since a cover of `lead oxide for the impure metal bath' is required. Litharge to be used in this process may be made in many different Ways and may vary in impurities somewhat. We have found that litharge can be formed rapidly and produced cheaply by stirring relatively pure lead and blowing in air to create oxidizing conditions.

When litharge is -added to a kettle of lead containing antimony (some silver may also `be present even in a detinned and de-arsenicked lead) and stirred with a high-speed mixer asv described above at a temperature of the order of 11005 1200 F., a fluid slag results in a few minutes which is comparatively silver-free and high in antimony. The reaction which occurs as a result of this stirring with litharge is apparently' as' Thus, antimonyfromA the lead reacts with the litharge to form an antimony oxide while a corresponding amount of lead passes into the lead bath. The antimony oxide formed combines with the remaining litharge to form a liquid slag and in a short time the system of lead-antimony slag and lead-antimony metal reaches a point of equilibrium after which the above replacement reaction ceases. In commercial practice, according to the equation set forth in this paragraph, the amount of litharge present on the bath will preferablynot exceed that'required to remove the desired amount o! antimony from the bath. For instance, as shown in Fig. 4, when the litharge slag has absorbed sufficient quantity of antimony from the bath so that the slag then has an lantimony contenter more than about 15%, absorption ol' further antimony from the bath will depend on the original antimony content of they bath. For example, if the lead-antimony. slag has absorbed sulcient antimony from the bath -so that the bath contains, say, 5% of antimony, the slag will be in equilibrium with that bath when the slag contains, approximately, 46% antimony. Under this condition of equilibrium,

no more antimony will be absorbed from the bath into the slag. Similarly, we have found that lead-antimony slags containing other higher and lower proportions of antimony are in equilibrium with the antimony in the impure lead bath and no absorption of antimony from the bath into the slags at these equilibrium points will occur. These equilibrium points have been plotted on a curve designated as curve A in Fig. 4. The curves in Fig. 4 are based on data obtained by the actual practice of our invention Within our preferred temperature range, namely, between 1100-1200o F. Curve A may be employed to determine what content of antimony a slag should have to extract metal froma bath of given antimony content and vice versa. Curve B shows the content of lead in the litharge slag corresponding to a given antimony content as shown on curve A. Curves C and D are employed similarly to curves A and B for determining, respectively, antimony and lead where soda ash and litharge are employed instead of litharge alone. The curves as plotted are on the basis of tinandarsenic-free slags. If arsenic or tin were present, allowance would have to be made for them as both replace antimony in the slags.

In practising 'our invention, impure lead containing antimony and preferably already free of aresnic, is placed in the kettlefl, the lead is melted and heated to a temperature of the order of 1100-1200 F. and a quantity of litharge is placed on top of the molten metal. The highspeed electric stirrer is started and the litharge is mixed withl the molten metal. The litharge quickly reacts with the antimony and forms the iiuid lead-antimony slag until equilibrium is reached. At this equilibrium point, if there is still antimony present in the metal as determined by analysis, the slag may be withdrawn from the kettle and fresh litharge or lead-antirnonyslag applied inaccordance with Fig. 4. The removal of antimony will then proceed rapidly until a new equilibrium exists conforming with the now lower antimony content of -the metal bath. The lower the antimony content of the bullion at the time the slag is withdrawn, the lower the antimony concentration of the slag will be. 'I'he lead-antimony slags are then preferably placed on a lead bath having a high antimony content to build up the antimony content of they slag. By following this method, slags containing over antimony have been made.

The rate at which antimony can be recovered from lead in accordance with our invention is largely dependent on the rate at which lltharge can be added to the kettle and heated tothe temperature necessary for rapid reaction and then dispersed in the lead bath. A pre-determined amount of litharge maybe added to a kettle containing unsoftened lead and stirred into the lead at a temperature of 1100 to 1150e F. so that with the proper relation of kettle diameter to stirrer diameter such as for example as shown in Fig; 1, and enough antimony present, it is possible to remove 2 to 3% of antimony in 10 to 20 minutes.

The intimate contact between lead oxide and metallic lead arsenic and antimony caused by lished after about 10 to 30 minutes with the usual lead-antimony bullions used. The average rate of removal of antimony by our process in softenlbs. per hour per ton of metal in the kettle. Thisis equivalent to about 2800 lbs. per hour ona 40-ton kettle charge when operating at about 1100 F. and stirring speed of 1700 R. P. M. using a kettle about 86" in diameter and a stirrer 10 inches in diameter. about inches for a 40-ton kettle. For smaller or larger kettles, the impeller diameter will vary accordingly for good results.

In accordance with our invention, antimony may be removed from lead with the addition of litharge when stirring at speeds lower than the 900 R. P. M. mentioned above, and by maintaining temperatures lower than indicated above; but the rate of removal is slower and the slags not as high in antimony content, especially under certain conditions such as when using lumpy litharge. In our preferred method of operation,

We prefer an impeller of We use the high speeds of around 1700 R. P. M.

and temperatures around 1100 F. with litharge or slag substantially free from lumps.

Instead of litharge or lead-oxide slag, We have found that soda-ash and litharge or slag may be added to the kettle to form a sodium compound with antimony and thereby reduce the amount of lead in the slag. The replacement reactions proceed as indicated in the above reaction. Soda ash can be added at the beginning with litharge or it can be added after the lead-antimony slag has become molten. The use of soda ash in quantities theoretically necessary to form sodiumantimony compounds with all of the antimony oxidized by the litharge, will cause a new equilibrium to be set up between the antimony and lead in the slag .and the antimony in the bullion. Generally, the soda slag is more fluid than leadantimony slag and can hold more impurities and still remain fluid. Due to the high specific heat of soda ash and since the formation of sodium antimonate is an endothermic reaction, more heating is requiredthan when lead-oxide without soda ash is used, which' gives a slightly exothermic reaction with antimony.

When using soda-ash, the operating temperatures are thesame as when using litharge alone. However, soda slags remain gummy around 900 F., while litharge slags freeze at about l000 F.

'Curves C and D of Fig. 4 referred to, show the results obtained in a series of tests using sodaash with litharge and may be used to determine what content of antimony the bath and slag should have in a similar manner to curves A and B. It appears that with lead containing up to about 40% antimony, the antimony contents of the slag are about the' same. After that, howtent, but in all cases they are lower in lead content so that the ratio of antimony to lead is increased. For example, when antimony in lead being softened is 5%, which is not uncommon for blast furnace bullons, a lead-antimony slag made by our process using litharge Without soda would contain about 46% antimony and .42% lead. If now the same lead-antimony slag is returned to the same sort of molten bullion containing say 5% antimony and the requisite amount of soda-ash added, the resulting soda lead-antimony slag will contain about 49% antimony and only 21% lead as shown in Fig. 4, curve D. Thus the soda slag not only contains more antimony but one-halfl of the lead will have been precipitated from the original slag. y'I'he antimony to lead ratio has been reduced from l to .92 down to l to '.43. This means that if the lead-antimony slag were -reduced to metal, the resulting alloy would -contain 52% antimony, whereas the soda slag after removal of the soda would make an alloy containing antimony.

The following examples represent preferred embodiments of the invention. It is to be understood that these examples are illustrative and the invention is not to be considered as limited thereby except as indicated in the appended claims.

Example 1 This example illustrates the softening of antimonial lead 'by first producing a lead-antimony slag of relatively low antimony content which is vthen built up to a high antimony content by stirring thel slag into a second bath of fresh metal.

400 lbs. of litharge was added to '7,860 lbs. of

Metal treated Removal stirring Antim ony rate time removed, pounds Sb (minutes) Weight, Per cent Pounds pounds per hour pounds Sb Sb per ton Start, 0 7, 860 l. 20 94 78 79 7,800 .21 16 The 490 lbs. slag from the above test was charged on to 7,300 lbs. of lead bullion. After stirring at 1700 R. P. M. for l5 minutes at 1160 F., a liquid slag weighing 365 lbs. and containing 38.50% Sb was removed. The metal after treatment carried 1.88% Sb and was thus about inV equilibrium with the slag in accordance with said' curve A. The results are as follows:

` Metal treated Removal Stirring Antimony rate time removed, pounds Sb (minutes) Weight, Per cent Pounds pounds per hour pounds Sb Sb per ton Start, 0 7, 300 2. 79 204 65 71 7,402 1.88 139 Example Z This example shows the removal of antimony to low percentages from a lead bath already low in antimony vcontent by using a litharge containing an appreciable amount of antimony.

To 7,860 lbs. of lead containing .48% Sb Was added 255 lbs. of litharge assaying 7.2% Sb. This was stirred at 1700 R. P. M. Afor 15 minutes at a temperature of 1l50 F. A liquid slag weighing 151 lbs. and containing 21.7% Sb was removed, leaving a metal assaying .15% Sb which was approximately'in equilibrium with the slag. Rate of Aantimony removal for this test was 15 lbs. per hour per ton. This slag containing 21.7% antimony would be used to produce a slag with a con- "Example 3` This example shows the effect of adding soda ash with the litharge in our process for removing arsenic an'd antimony.

480 lbs. of litharge and 80 lbs. of NazCOs.

added with 140 lbs. of soda ash and stirred for 60- minutes as before, the temperature varying between 1120 and 1160 F. The slag was a little pasty, so 9 lbs. of salt was added which increased the fluidity. 550 lbs. of slag were skimmed on' which assayed 43.06% antimony and only 22.4% lead. 3.43% of antimony remained in the metal. This shows that little more antimony was removed because an equilibrium practically existed for antimony, but the lead in the slag added was reduced by soda from 39.6% to 22.4%,

The lead in the kettle now weighed 6,980 lbs.

The rate oi antimony removal during the rst 30 minutes of the run was 114 lbs. per hour per ton on the metal basis.

Example 4 In Example 3,v the lltharge and soda ash were added together. In this run the litharge was added alone iii-st, and after this was stirred and became liquid, the soda ash was added.

To 84,000 lbs. of lead bullion containing 5.57% Sb was added 2,700 lbs. of litharge. After stirring for 20 minutes at 1700 R. P. M. and a temperature of 1100 to 1150"- F., the `slag was liquid. It contained more than antimony. 342 lbs. of soda ash were now gradually added while stirring which required 50 minutes at the end of lwith litharge; the other 70 minutes being used to replace the lead in the slag with soda by stirring in the soda ash.

The rate of removal during the iirst minutes was 58 lbs. per hour per ton based on metal analysis.

The lithargeslags obtained by the above examples have a high antimony content ranging upwards to over 70% antimony. These slags may be treated to recover antimony as antimonial lead or otherwise to recover the antlmony.

The process as described is a highly eiiicient method particularly for the removal vof antimony from lead and the production of high antimony dresses and operates at a relatively high speed of removal and low cost.

' What we claim is:

1. A process for removing antimony from impure lead containing antimony but substantially no tin which comprises, placing a quantity of lead oxide containing not less than 15% of antimony as oxide on a bath of the impure lead in molten 'condition containing not less than 4% i antimony, said quantity of lead oxide being sufcient to reduce the quantity of 'antimony in said bath to not less than about 1.9% antimony, stirring the molten impure lead and lead oxide at a temperature of the order of 1100-1200 F. to produce a molten slag containing antimony absorbed by the slag from the bath and discontinuing the stirring and removing the slag when an equilibria um is reached, that is, when the antimony content of the slag has reached not less than about 38.5% antimony as oxide and the antimony content of the metal is not less than about 1.9%.

2. A process for removing antimony from impure lead containing antimony but substantially no tin which comprises, stirring the impure molten lead containing from 0.5%-2.5% of antimony with litharge at a temperature of the order of. 1100-1200 F. to produce a molten slag containing lead oxide and not less than 15% antimony as oxide removed from the impure lead, stirring a quantity of the slag so produced containing not less than 15% antimony into a second bath of impure lead containing not `less than 4% antimony at a temperature of the order of 1100-200 F., said quantity of slag being suincient to reduce the content of antimony in the bath to not less than about 1.9% and discontinuing the stirring and removing the slag when an equilibrium is reached, that is, when the antimonvV content of the slag has reached not less than about 38.5% antimony as oxide and the antimony content of the metal is not less than about 1.9%.

3. A process for treating impure lead containing `arsem'c and antimony but which is substantially free from tin which comprises, removing the arsenic substantially entirely by a preliminary treatment, placing a quantity of lead oxide containing not less than 15% of antimony as oxide on a bath of the impure lead in molten condition containing not less than 4% antimony,

said quantity of lead oxide being sufficient to reduce the quantity of antimony in said bathto not less than about 1.9% antimony, stirring the molten impure lead and lead oxide at a temperature of the order of 1100-1200 F. to produce a molten slag containing antimony absorbed by the slag from the bath and discontinuing the stirring and removing the slag when an equilibrium is reached, that is, when the antimony content of the slag has reached not less than about 38.5% antimony as oxide and the antimony content of the metal is not less than about 1.9%.

4. A process for removing antimony from impure lead containing antimony with substantially no tin which comprises, taking a. molten bath of the lead containing not less than about 1.9% antimony and a molten slag of lead oxide and antimony oxide containing not less than about 38.5% antimony as oxide, and mixing sodium carbonate with the molten slag at a temperature of the order of 1100-1200 F. to reduce the amount of the lead in the slag.

5. A process for removing antlmony from impure lead containing antimony but substantially no tin which comprises, placing a quantity of lead oxide containing not less than 15% of antimony as oxide on a bath of the impure lead in molten condition containing not less than 4% antimony, said quantity of lead oxide being suicient to reduce the quantity of antimony in said bath to not less than about 1.9% antimony, stirring the molten impure lead and lead oxide at a temperature of the order of 1100-1200 F. to produce a molten slag containing lead and antimony absorbed by the slag from the bath, discontinuing the stirring and removing the slag when an about 38.5% antimony as oxide and the antimony` content of the metal is not less than about 1.9%, and mixing soda with the slag to reduce the amount of lead therein.

6. A process for removing antimony from impure lead containing antimony but substantially no tin which comprises, placing a quantity of lead oxide containing not less than 15% of antimony as oxide together with soda on a4 bath or the impure lead in molten condition containing not less than 4% antimony, said quantity of lead oxf ide being sumcient to r'educe the quantity of antimony in said bath to not less than about 1.9%

antimony, stirring the molten impure lead, lead oxide and soda at a temperature of the order of 1100-1200" F. to produce a Amolten slag containing antimony and lead, and discontinuing the stirring and removing the slag when an equilibri- WALTER T. MONSON. HAROLD L. HUMES. RICHARD P. E. HERMSDORF. 

